Electrodynamic transducer and method of manufacturing same



June 23, 1970 K. SCHNEIDER 3,516,151

ELECTRODYNAMIQ TRANSDUCER AND METHOD OF MANUFACTURING SAME Filed July 14, 1966 INVENTOR. KUNO SCHNEIDER BY w AGEN United States Patent Ofiice 3,516,151 Patented June 23, 1970 3,516,151 ELECTRODYNAMIC TRANSDUCER AND METHOD OF MANUFACTURING SAME Kuno Schneider, Vienna, Austria, assignor, by mesne assignments, to US. Philips Corporation, New York,

N.Y., a corporation of Delaware Filed July 14, 1966, Ser. No. 565,252 Claims priority, application Austria, July 16, 1965, A 6,557/65 Int. Cl. H04r 7/02 US. Cl. 29 594 10 Claims ABSTRACT OF THE DISCLOSURE A method of manufacturing an electrodynamic transducer and the resulting product wherein the neck edge of a diaphragm cone is connected to the axially spaced and adjacent moving coil, by supporting the cone and coil on a mandril, spraying a thermoplastic material that forms an abridging cylindrical layer between the cone and coil, heating the material, and removing the mandril.

In electrodynamic transducers it is essential that the part of the vibrating system extending in the magnetic system, that is to say, the moving coil and the throat of the diaphragm to which it is secured, have the lowest possible weight. In addition it is of importance that the coupling between the moving coil and the diaphragm is very rigid. To fulfil these requirements the invention provides a particularly simple and advantageous solution.

According to the invention the throat portion of the diaphragm forming the connection with the moving coil consists of a hardenable synthetic material, for example, an epoxide resin, a thermosetting plastic. When in such a transducer the diaphragm is centered by a centering ring, according to the invention the inner edge of the centering ring is embedded in the hardenable synthetic material of the part of the diaphragm forming the connection with the moving coil.

The invention further provides a method of manufacturing a diaphragm assembly for such an electrodynamic transducer, the term diaphragm assembly being understood to mean herein the vibrating system consisting of the moving coil, the diaphragm and possible centering means.

According to the invention such a diaphragm assembly is manufactured so that on a mandril, which is provided with separating means and preferably consists of two parts, prefabricated parts of the diaphragm assembly, for example, the moving coil, the diaphragm cone and the like, are arranged in the mutual position corresponding to the finished assembly, the non-covered parts of the mandril being then sprayed with a hardenable synthetic material, for example, an epoxide resin, the synthetic material being then hardened for a short period of time by suitable supply of heat, for example, through the mandril, and the diaphragm assembly being then removed from the mandril. It has proved of particular advantage if the hardenable synthetic material is sprayed in powder form since in this case particularly even and rapidly hardening layers can be obtained.

It has further been found to be of advantage, particularly for a fully automatic series production, if a stationary mandril is kept at the temperature desired for hardening the hardenable synthetic material by means of a thermostat, the spraying of the hardenable synthetic material on the mandril being efiected by a spraying device moving around the mandril. Spraying of the mandril with hardenable synthetic material is preferably carried out by means of several nozzles, which are arranged around the mandril and are collectively moved concentrically about the mandril to obtain an even layer thickness on the mandril. For a particularly economic performance of the above described method it is of advantage to remove excessive hardenable synthetic material laterally from the spraying device by means of an exhaust device. This excessive synthetic material may then be recovered. As a result of this also the region within which the hardenable synthetic material is provided, is laterally very readily bounded, so that not unnecessarily much synthetic material is deposited on the moving coil or the diaphragm cone.

In a particularly simple embodiment of the method it has proved of advantage to wind the moving coil, preferably without a support, immediately on the mandril on which the prefabricated parts of the diaphragm assembly are arranged.

In the above described manner electrodynamic transducers can be obtained, which have very good electroacoustic properties and can be manufactured in a very simple manner. It has also been found that such transducers can be subjected to very high loads and have very good properties as regards life.

In order that the invention may readily be carried into effect, it will now be described in greater detail, by way of example, with reference to a few embodiments which are shown partly diagrammatically in the drawing, but the invention is not restricted to these examples.

FIG. 1 shows, partly in section, an electrodynamic loudspeaker in which the diaphragm is centered by means of a centering ring,

FIG. 2 shows a diaphragm assembly destined for a loudspeaker without centering ring, the assembly being still on the mandril on which the hardenable synthetic material was provided; the method of manufacturing will also be described with reference in this figure.

FIG. 3 shows a diaphragm assembly for an electrodynamic microphone.

FIG. 1 shows an electrodynamic loudspeaker the diaphragm 1 of which is secured to the loudspeaker housing 3 by means of the mounting member 2 and is centered with respect to the magnetic system 5 by means of a centering ring 4. The magnetic system comprises an air gap 6 in which the moving coil 7 is arranged. Said moving coil is constructed in known manner without a support; for this purpose it is wound so that one turn engages the other and a wire is used the insulation of which is softened at a given temperature and joins the insulation of the adjacent turns. According to the invention the connection between the moving coil 7 and the diaphragm 1 as well as the centering ring 4 is formed by a diaphragm throat 8 which consists of a hardenable synthetic material. Since said synthetic material is very light and at the same time very stiff, a vibrating system having very good electro-acoustic properties is obtained. In fact, optimum use may be made on the one hand of the crosssection of the air gap in the magnetic system, since no additional parts are required for connecting the throat of the diaphragm and the moving coil, and, on the other hand, the diaphragm throat of synthetic material forms a very good coupling between the moving coil and the diaphragm cone.

The connection wires for the moving coil, one (9) of which is shown, are conducted in normal manner away from the moving coil along the side of the diaphragm cone 10 facing the axis of the loudspeaker. The wires are then passed through a small hole in the diaphragm cone and connected to soldering lugs 11 on the loudspeaker housing 3. In the area of the diaphragm throat 8 they are embedded in the synthetic material. Of course, if required, said connection Wires may also be conducted on the other side of the diaphragm; alternatively the construction of the moving coil itself may be carried Out in 3 a variety of manners, and, as shown, for example, in FIG. 1, a dust hood 23 may be provided.

As regards the hardenable synthetic material from which the diaphragm throat is formed, several such products which are commercially available may be used without leaving the scope of the invention. For example, epoxide resins are very suitable. Excellent results were obtained, for example, with the hardenable synthetic material obtainable under the trade name Scotch Cast.

The method of manufacturing a diaphragm assembly without centering ring will now be described with reference to FIG. 2. 011 a mandril 12 comprising separating means and formed by two parts 13 and 14, a moving coil 7 is wound without a support. Then the diaphragm cone 10 is provided on the mandril, the moving coil and the cone being arranged already in the position, which corresponds to the finished diaphragm assembly. As shown in FIG. 2 this is reached in that the moving coil is wound on a thinner portion of the part 13 of the mandril, which portion is at the correct distance from the conical part 14 of the mandril on which the diaphragm cone is laid.

Hardenable synthetic material in powder form is now sprayed concentrically on the said arrangement by a nozzle 16 shown diagrammatically. The mandril 12 is at a temperature at which the synthetic material is hardened in a short period of time. Two laterally arranged nozzles 17 and 18 draw off the excessive synthetic material during spraying the mandril. In accordance with the intensity in which this drawing off is carried out, and the manner in which said nozzles are arranged, respectively, the extent of the regions 19, 20 within. which synthetic material is deposited on the moving coil and the diaphragm cone, respectively, can be influenced. Said regions are preferably constructed so large only that just the required rigidity of the connection between the synthetic material and the adjacent parts is obtained. Simultaneously the excessive synthetic material is recovered so that the method is very economic. In this manner a layer of hardened synthetic material is formed on the mandril 13 which layer forms the diaphragm throat 8 and effects the connection between the moving coil and the diaphragm cone. By suitable choice of the duration of the spraying method, the thickness of the layer of syn thetic material may be chosen arbitrarily within wide limits.

The heating of the mandril 13 to obtain the desired hardening temperature is effected in the embodiment shown in FIG. 2 by a heating member inserted in a recess 21 of the mandril. Preferably the mandril is constantly kept at the same temperature. Alternately it may be heated to the said temperature periodically only during each spraying process. Of course other possibilities of supplying the required heat may be used.

As soon as the synthetic material in the required thickness is hardened, the diaphragm assembly is finished and may be removed from the mandril. This is simply effected by displacing the part 13 of the mandril in the direction of the arrow 22. The removal is preferably eifected while the mandril is warm since then the diaphragm assembly can easily be detached from it.

In order that the mandril is concentrically sprayed with synthetic material, the nozzles 16, 17, 18 are moved around the mandril. Preferably several such sets of nozzles are arranged around the mandril and moved collectively within regions which, for example, overlap each other. Of course, it would also be possible for the nozzles to be stationary and the mandril to be rotated.

In the present example the synthetic material was provided by spraying and simultaneous hardening, but of course it would alternatively be possible to provide the synthetic material by an electrostatic process followed by hardening. The method according to the inventon is not restricted to a hardenable synthetic material in powder form, but alternatively, as is known, synthetic material starting from material in rod form may be sprayed, or in general hardenable synthetic material in the liquid condition may be used.

The method of manufacturing according to the invention, however, may also be varied in other respects without leaving the scope of the invention. For example, the diaphragm cone may first be arranged on the mandril and then the moving coil be wound or a finished moving coil may be arranged on the mandril, and the like.

FIG. 3 finally shows a diaphragm assembly for another type of electrodynamic transducer, namely for an electrodynamic microphone. The diaphragm is denoted by 1 and the moving coil by 7. The connection between the two members is formed by the diaphragm throat 8 consisting of hardenable synthetic material which in such arrangements usually has a very short construction. Therefore, such a short throat will be manufactured with one or several of the narrow nozzles according to the method described above.

What is claimed is:

1. A method of manufacturing a diaphragm assembly for an electrodynamic transducer having a diaphragm cone and a moving coil, comprising the steps:

'(a) disposing the diaphragm cone and the moving coil coaxially on a mandril,

(b) positioning the cone to have the edge of its neck end axially spaced from and adjacent one edge of the coil,

(c) connecting said cone edge and the coil, by applying a thermosetting plastic material therebetween and contacting same,

(d) heating said material and thereby curing it to a substantially rigid state, and

(e) removing said mandril.

2. A method of manufacturing a diaphragm assembly as defined in claim 1, wherein said cone and coil are axially spaced to expose a portion of the mandril therebetween, and applying the thermosetting plastic material comprises spraying the material from at least one nozzle subassembly, circumferentially about said mandril portion and the adjacent cone and coil.

3. A method of manufacturing a diaphragm assembly as defined in claim 2, comprising the further step of establishing relative rotation between the cone-coil-andmandril subassembly and the nozzle subassembly by rotating one of these subassemblie-s about the mandrils axis, for obtaining a generally uniform thickness of said sprayed material.

4. A method of manufacturing a diaphragm assembly as defined in claim 2, comprising the further steps of drawing 011 by suction excess material sprayed by said nozzle subassembly.

5. A mtehod of manufacturing a diaphragm assembly as defined in claim 2 wherein said heating and thermosetting plastic material comprises energizing a heating ele ment axially disposed within the mandril.

6. A method of manufacturing a diaphragm assembly as defined in claim 2 wherein said thermosetting plastic is a powder.

7. A mehod of manufacturing a diaphragm assembly as defined in claim 2 wherein said thermosetting plastic is a liquid.

8. A method of manufacturing a diaphragm assembly as defined in claim 2 comprising the further step of centrally supporting said cone by including on a mandril a conical member corresponding in shape to the cone and closely adjacent thereto.

9. A method of manufacturing an electrodynamic transducer as defined in claim 1, wherein the connecting step (c) comprises forming a cylindrical layer of sprayed thermosetting plastic material between and adjoining the edge of the cone and the spaced, adjacent coil, which are respectively embedded in said layer.

10. A method of manufacturing as defined in claim 9, further comprising forming a centering ring, axially dis- 5 I 6 posing said ring between the coil and cone, and em- 2,640,556 6/1953 Brennan W. 181-31 bedding its inner edge in said layer adjacent the edge of 2,408,038 9/1946 Brennan 264 -309 the cone. 2,540,450 2/1951 Keddie 1 81--32 2,596,364 5/1952 Brennan 181-32 References Cited 5 2,624,417 1/ 1953 Brennan 18132 UNITED STATES PATENTS RALPH D. BLAKESLEE, Primary Examiner 1,907,687 5/1933 Van Lis 179--115.5 Us Cl XR 1,969,256 8/1934 Clark 179115.5

2,392,143 1/1946 Graham 179-4155 10294061602;179*115-5;264-309 

